Mockingbird, aka Bobbi Morse, and Commodore Lance Hunter have a lot of things in common. They're both secret agents (Morse works for SHIELD, Hunter is the head of STRIKE). They both debuted in the 70s. And they both made their first appearances in England: Bobbi at the front door of Ka-Zar's mansion, Hunter in the pages of Captain Britain.
And that's about where their similarities end. They certainly don't have a similar number of appearances; Hunter has only shown up in a handful of issues since his debut, and the majority of those were in the spring of '77. Other than that, he's only appeared in a Civil War tie-in in 2007 and one issue of a miniseries involving Marvel UK characters called Revolutionary War in 2011. That is, until this month's Mockingbird: SHIELD 50th Anniversary Special #1 (September 2015). Which is the most important.
See, last year - for whatever reason - Lance Hunter became a recurring character in Agents of SHIELD season 2 (2014-2015). He wasn't the head of STRIKE; heck, he wasn't even a member of STRIKE, which in the MCU is an elite subgroup of SHIELD. He was just a mercenary. But he was British. And as a new wrinkle in his backstory, he took Hawkeye's place as Mockingbird's ex (as Hawkeye was in the movies and off-limits, and - as we'd later learned - married with kids anyway). Over the course of the season, we see them move slowly from angry exes to a love/hate relationship.
That relationship, at least to some degree, is now codified in the recently mentioned Mockingbird special. Whether it'll continue remains to be seen, but as Hunter seems to have been de-aged (no more combover) to more closely match his tv depiction, I think it's likely.