"I regret to say that we were late," HKEX boss Charles Li told an audience in London. "We had wanted to do this for quite a while."
He explained further that the company had been waiting to make a bid to combine with London's exchange operator while Brexit uncertainty dragged on.
Li even said he understood LSE Group CEO David Schwimmer's rationale in rejecting the Hong Kong deal, stating: "If I were in David's shoes, I would reject Charles Li."
He added that HKEX's logic in announcing the proposed transaction at the time was that it was "now or never" and that it had to "take some risks."
HKEX's chief was speaking just minutes after LSE's Schwimmer spoke on stage at the Sibos conference in London. In a snub to the HKEX deal, Schwimmer said that he viewed Shanghai, not Hong Kong, as China's "financial center."
He referred heavily to a scheme between London and Shanghai's stock exchanges that allows international firms to list their shares in mainland China.
The LSE has already agreed to buy financial data firm Refinitiv in a $27 billion deal which Schwimmer said would enable the firm to tap into foreign exchange trading and have an increased presence in fixed income.
But Li isn't backing down in his bid to merge the two stock exchanges.
"Together we complete each other," he said, adding that it would enable round-the-clock operations once the Hong Kong exchange is able to take advantage of trading during European hours.
The merger deal is less about finding cost synergies and more about benefiting from the "tidal wave of opportunities" such a move would bring, HKEX's boss added.