The phrase "a sincere friend of" is correct and usable in written English.
It can be used to describe someone who genuinely cares for and supports another person or cause.
Example: "She is a sincere friend of the environment, always advocating for sustainable practices."
Alternatives: "a true supporter of" or "a genuine ally of".
Rod was a sincere friend whose unsurpassed charm, wit and integrity will be sorely missed.
Veterans have a sincere friend and advocate in Mr. Blumenthal, but this is obscured by featuring a few infelicitous sentences said by him in a lifetime of accurate, publicly recorded statements.
Russian president Vladimir Putin called Castro "a sincere and reliable friend of Russia," while Chinese leader Xi Jinping said that "the Chinese people have lost a close comrade and a sincere friend".
That's why sincere friends of Egypt call on the government to drop the charges against him.
Selma and Walter were lifelong partners in supporting the Jewish Cadet Program at West Point and were sincere friends of the members of the United States Army.
The ascetics are described as those "who know the shortcomings [of the world], who crave for the hereafter and are convinced of it, firmly rooted in its science, that is the sincere Friends of God, [His] faithful servants, the cream of all [His] creatures, whom the Creator – may [He] be exalted – called 'persons of understanding, persons of view, persons of mind'" (I, 357, 5 9).
Yad Sarah, its volunteers in Israel and its friends in the USA note with profound sadness the passing of Ursula Merkin, a warm and sincere friend.
He was a good and sincere friend to the New Yorker, and he will be sorely missed - for his work had the rare and discomforting tingle of genius.
Kathryn says, "These are letters from the Rector to Barbara, which show absolutely perfectly that he was just simply taking care of her as he always claimed". Kathryn showed Inside Out a number of letters signed "your sincere friend and padre", written to a girl who claimed in court she never even knew he was a priest.
At the signing ceremony, Xie Zhenhua, China's vice-chairman of National Development and Reform Commission and the country's top climate change negotiator, tried to soothe such concerns: "We regard India as a sincere, devoted friend and the MoU [memorandum of understanding] on climate change will take our cooperation on the issue to a new high".
