Former Rep. Vito Fossella (R-N.Y.) will publicly endorse Republican Michael Allegretti at a press conference on Staten Island Friday morning, a source close to the Allegretti campaign told The Ballot Box. 

Allegretti is competing against former FBI agent Michael Grimm for the GOP nomination to face freshman Rep. Mike McMahon (D-N.Y.) in November. The rhetoric between the two Republicans has grown increasingly heated as the Sept. 14 primary approaches.

Fossella had been supportive of Allegretti since retreating from public life, but in the last few days decided to go public with an endorsement, the source said.

The backing could help Allegretti claim the nod. Fossella still holds considerable sway among Staten Island Republicans despite being forced into retirement last cycle after a 2008 drunken-driving arrest revealed he had a second family in the Washington suburbs. 

There was speculation he was planning a comeback in 2010 — he was even endorsed to run again in May by the Staten Island Republican Party executive committee. But Fossella declined, telling reporters, "I am frankly at a very good place in my life."

There were signs recently that he wasn't content with sitting on the sidelines. The six-term congressman announced earlier this month he would make a rare public appearance at a rally on Sunday protesting the mosque planned to be built near Ground Zero in New York City.

Fossella will announce his support for Allegretti Friday at the Great Kills Friendship Club on Staten Island.

—Updated at 7:38 p.m.